Black and odorous water and water eutrophication are common characteristics of water pollution. Long-time waste receiving has caused sediment deposition in water bodies such as rivers, pool ponds and canals. When the water quality is significantly improved or the water is disturbed, contamination constitutes in the sediment would release to the water, causing the sediment to be an inherent contamination source of the water body. Therefore, sediment management is fundamental to water quality improvement and key to solve water pollution problems. Exploration and development of sediment management techniques is imperative.
Currently, the main methods for sediment management include sediment dredging, chemical shielding and microbial remediation.
Sediment dredging mechanically removes contaminated sediment, clearing the inherent contamination source of a water body, which is the most commonly used method. However, this method is costly and includes steps of excavating, transporting, treating, disposing, and so on. Moreover, the disposal of the sediment may cause secondary pollutions such as unpleasant odor and leachate pollution.
Chemical shielding (or referred to as sediment capping) provides tremendous shielding materials upon the contaminated sediment to separate the sediment from the water body, so as to prevent nutrient contents, heavy metal elements and organic wastes in the sediment from entering into the water body. For example, CN 200710191195.2 disclosed a method for capping eutrophicated sediment in which a large amount of clay shielding materials and additives were used. These materials were subject to pretreatment including grinding, sieving, and high-temperature baking. When fed to the water body, these materials can only prevent the release of nutrient salts such as nitrogen and phosphate and algal blooms, failing to fundamentally resolve pollution problems. Contaminated sediment would still be formed over time due to the deposition and accumulation of the contaminants in the water body.
Microbial remediation in-situ degrades the contaminants in the sediment into CO2 and water or converts the sediment to non-harmful substance by utilizing naturally occurring or cultivated microorganisms. This method is not a simple separation or transfer, but in-situ elimination, of contaminants, and has advantages including low cost, easy implementation, good effect, less environmental disturbance, high safety and reliability.
Sediment of water body has a high content (2 to 45%) of organics which is the main reason of sediment anaerobic digestion and poor water quality. These three methods currently used are directed to the transfer or in-situ elimination of the contaminants in the sediment with the aim to reduce the COD therein, without considering transformation, collection and utilization of the biomass energy enriched in the sediment, resulting in waste of the energy.
In recent years, microbial fuel cell (MFC), as a new technology resulted from combination of microbiology and cell technology, is fast developing. MFC is a device that directly converts chemical energy in organics into electric energy using microorganism as catalyst, and has a dual function of power generation and waste treatment. The basic principle of MFC is summarized as follows. Organics, serving as fuels, are oxidized by microorganisms to release electrons and protons in anaerobic anode chamber. The electrons are transferred to the anode and further to the cathode through external circuits, thus a closed loop is formed and current is generated. The protons are transferred to the cathode through an ion exchange membrane, and react with oxygen to generate water.
In addition to high concentration of organic waste water, MFC can also use domestic sewage, animal manures and etc. as fuels to generate electricity. Therefore, MFC is an advanced biomass energy utilizing technique with huge development potential and is expected to become a key technique in organic waste treatment in the future. CN 200510011855.5 and CN 00810805.6 disclosed a single-chamber microbial fuel cell for treating organic waste and a dual-chamber microbial fuel cell for treating waste water and active sludge, respectively. These cells, however, are laboratory scale cells with open circuit voltage not more than 0.8 V. These documents didn't mention the expansion and enlargement of multiple cells. CN 200810029221.6, filed in the name of the assignee of the present invention, disclosed a microbial fuel cell stack which is a multi-stage series/parallel MFC cell stack sharing a common anode fuel. The provided cell stack unified the out/in of fuels, provided an increase in voltage/current, and achieved the expansion and enlargement of microbial fuel cells. However, the cell stack is still only suitable for using aqueous or slurry type organic wastes with low solid content and good flowability as fuels. The fuels are pumped to the anode chamber of the cell stack and subject to biological oxidation for power generation and elimination of COD, and then flowed out, for the purpose of both treatment and power generation.
The microbial fuel cells mentioned above, however, are not suitable for sediment treatment, because of the following reasons. First, the sediment should be pumped to the anode chamber of the MFC, which constitutes extremely large work load. Moreover, this is difficult to realize in the presence of superjacent waters, and the sediment cannot be treated in-situ. Second the sediment has a high solid content, the particulates in which are easy to cause blockage. Third, in order to achieve in-situ treatment, MFC must be immersed into the sediment such that the sediment is in contact with the anode. The cathode of conventional MFC would not expose to air if the cell is immersed in water body, the oxidation-reduction reaction thus would not happen at the cathode. These existing technical problems make the conventional MFCs not able to be directly used for sediment treatment and clean electricity generation.
No report regarding sediment treatment using microbial fuel cell technology with simultaneous electricity generation is found in the prior art.